My father is attempting to add another room in our basement back home, roughly 4 hours away from me (wood framing only). He wants to heat this new room, obviously but isn't sure of the best way to do it. There is a heat duct that runs right outside one of the interior separation walls that he's going to tap into and run heat from. This room won't be used all the time so it's not necessary to heat it at all times - meaning he wants to be able to shut off the heat source to that room when he can. Does anyone have any ideas? He used to be a carpenter so he's well informed about how to build the room itself he just doesn't have much experience in heating or adding a new heat duct. Any ideas or advice will be appreciated, thank you!

Tying into an existing heat run is often done, but sometimes with mixed results. Marginal examples I've seen in basements usually tap in at ceiling height instead of down at floor level (to save a few nickels on sheet metal), and often have forgotten to include a cold air return. Most big box stores sell adequate off-the-shelf sheet metal products, including register grills that open and close, to help your Dad. If the existing plenums serve a lot of upstairs rooms, there's the possibility that the farthest away from the furnace will feel the result of less available heat and additional "junk air" in the supply plenum. If the furnace is working at capacity now, possibly an alternate heat source should be considered, such as a baseboard heater or two. Might be worthwhile to have a qualified heating contractor take a look at things, picking his brain for the best approach to use (either using his services or DIY).

If the new room is going to be used as a bedroom, don't forget that adequate egress is required. Also, tell Pop he needs to adequately insulate the new room--walls, ceiling and floor (if possible).

Thank you for the suggestions. He's very familiar with the construction process, including the insulation. It's not a bedroom, just a spare room so no egress is needed. Thank you for the concern, though.

If he only wants heat when he is going to be in the room, I would use electric with a 2 pole switch in the main living area so he can turn it on ahead of time. If he uses a switch with an indicator light, he would be reminded to turn it off.